This invention relates to can closing machines. Specifically this invention relates to a double seam forming can closing apparatus which identifies defects and rejects cans with improper seams. This invention further relates to a double seam forming can closing apparatus in which the seam forming parameters may be set up more rapidly and reliably.
Canning equipment and processes are commonly used in a variety of industries. Canning processes are often used to preserve food products because such products can be processed and promptly hermetically sealed within a can. Canning operations may be performed at high speed and at a reasonable cost. The sealing of cans is important because an improper seal may result in the infiltration of air to the interior of the can. This may result in bacterial growth and premature spoilage.
Can closing machines are known in the prior art. One type of can closing machine secures an end to a can body after the product has been placed in the can by formation of a folded double seam. An example of a double seam forming machine which secures top ends to can bodies is shown in U.S. Pat. No. 3,465,703. The disclosure of this Patent is incorporated herein by reference.
The goal of a double seam forming machine is to produce a perfect seam which extends about the circumference of every can that passes through the machine. Unfortunately this is not always possible. Undesirable conditions may occur due to defects in either the can body or the can end. Such defects may include undesirable variances in dimensions in which the ends do not perfectly xe2x80x9cfitxe2x80x9d the can bodies. Variations in metal thicknesses may also occur which impacts the ability to form a proper double seam.
Other conditions which may cause imperfect seams include cracks or tears in the can bodies or can ends. Such defects may result in loose or open spaces in the seam. Similarly, defective manufacture of the ends or bodies may result in folds or areas having excessive metal thickness. Such defects in the area of the seam also prevent proper seam formation.
Defects in the chucks or rolls which are used to form the seams can also result in defective can seams. Such defects may include the accumulation of metal on a chuck or roll. The accumulated material causes irregularity in the tooling surface in contact with a seam as it is being formed and can result in an improper seam. Alternatively the-chucks or rolls used to form the seam may crack, producing a gap. The seam is not properly formed in the area of the gap which results in improper can closure.
Double seam can closing machines generally include several stations where cans are formed. They include multiple associated sets of chucks and rolls which perform the same operations. If a tooling problem occurs at one chuck or roll, it will not be readily apparent because only cans that have been acted upon by the defective tooling will exhibit an improper seam. Double seam forming machines typically operate at very high production rates. It is therefore difficult to detect a problem as soon as it occurs. Hundreds or thousands of cans that are potentially defective could be closed before a problem is noticed.
In an effort to improve the inspection of can seams produced by a double seam can closing machine, others have developed devices to monitor seam quality. An example of such a device is shown in U.S. Pat. No. 4,600,347, the disclosure of which is incorporated herein by reference. This Patent discloses a modification to a standard can closing machine in which force sensors are installed on a stationary cam. Cam followers move around the stationary cam in engaged relation therewith. The cam followers are in connection with the rolls which contact the can ends and chucks which form double seams. The contour of the cam moves the cam followers, which in turn move the rolls to form the seams.
In the prior art device the sensors on the stationary cam detect the force applied by the cam followers during the final ironing turn of the can seam before the can leaves the machine. The force applied to the stationary cam by each cam follower during this operation corresponds to the configuration of the formed can seam about its circumference. The prior art device works on the principle that by monitoring the force applied by the cam follower for each station as it performs the final ironing turn on the seam, certain defects can be identified. Common defects include situations where the seam is either too tight or too loose. Such defects may arise in the form of a consistently high or low force or a transient force xe2x80x9cspikexe2x80x9d. A high transient force spike indicates excessive metal on either the can seam, forming roll or a tooling chuck. Alternatively, a transient low spike may be indicative of a cracked tooling roll or chuck, or a gap or tear in a can seam.
While the device shown in U.S. Pat. No. 4,600,347 represents a significant advance in the detection of seaming problems, it suffers from several drawbacks. These drawbacks include the fact that double seam forming can closing machines generally include many stations. The tooling associated with each can closing station is somewhat different. This results in variation of the force that is applied by each cam follower as it moves across the force-sensing portion of the stationary cam. As a result, the amount of force associated with a xe2x80x9cgoodxe2x80x9d seam in different stations can vary significantly. The prior art devices cannot account for this variation in normal loading between the various machine stations. Rather, the prior art generally compares the applied seam force to a single high limit or low limit for all the stations. These limits must have a range that accommodates the force at all machine stations. An improper fault indication may result if the limits are set too narrowly. However, if the limits are set too widely then defective cans may be allowed to pass.
A further drawback associated with the prior art is that force variations that result from excess metal or a broken seam or chuck, are only detected if the corresponding spike is sufficiently xe2x80x9chighxe2x80x9d or xe2x80x9clowxe2x80x9d to extend beyond the limits which are established for a tight or a loose seam. Spikes or breaks that occur within the limits may be indicative of a developing tooling problem and/or have adverse consequences for the seam. However, in the prior art such conditions may go undetected.
A further drawback associated with the prior art is that developing problems with tooling, can bodies and can ends often go undetected until one of the limits is exceeded. Dimensional changes in the seam may begin moving the seam tolerances toward a limit. Such movement of seam conditions away from the optimum, increases the risk of seam failure. It may be advisable to correct such problems before they result in a fault condition. Unfortunately because the prior art devices cannot account for variations from station to station, such trends are difficult to detect.
Can seamers usually run at high speeds. As a result if a single can exhibits a fault condition, it is necessary to either shut the machine down or to locate the defective can among a large population of good cans. Stopping the machine delays production which increases costs and requires a set-up person""s attention for restart. Alternatively, not shutting the machine down while attempting to locate the can that is defective may be very time consuming. Visual inspection often may not readily distinguish a defective can which further complicates the problem.
A further drawback associated with the prior art systems is that they may be subject to false triggering. Vibration or other conditions may result in short-term xe2x80x9cnoisexe2x80x9d from the sensors on the stationary cam. This noise may produce a signal which falls outside the high and low limits, which causes a fault indication to be given. Considerable effort may then be expended in an effort to locate a problem that does not exist.
A further drawback associated with such prior art systems is the time necessary to set up the system. Generally such set-up requires the observation of sensor output signals produced by a number of cans with good seams. These seam xe2x80x9cprofilesxe2x80x9d must be observed and documented for each of the several stations of the machine. This task is complicated by the fact that sensor signals for a good seam can vary from station to station as previously discussed. Once the various seam profiles and force levels have been studied for a number of good cans passing through each of the stations, it is then necessary to set the high and low limit values at levels sufficient to accommodate the variation in force applied by the cam followers for numerous seams. The high and low limits must be set far enough apart so that frequent false indications are not given. This process of observing seam profiles for numerous documented good seams at each of the numerous stations on the double seam forming machine is time consuming.
A further drawback associated with the prior art systems is that the instrumented portion of the cam is ideally relatively flexible compared to other portions of the cam. This is done for example as shown in U.S. Pat. No. 4,600,347 by providing a slit which extends radially between the instrumented portion of the cam and the main portion of the cam body. This enables the instrumented portion to more readily deform. An indication of the applied force is obtained using strain gage type sensors.
Making the instrumented portion of the cam more flexible also reduces its strength. There is a risk that the instrumented cam portion may fracture or take on a permanent set due to the application of excessive force. Such excessive force may result from a situation where additional metal is present on a can, roll or chuck. Damage to the cam generally necessitates cam replacement. This is costly and time consuming. Further costs may be associated with production downtime.
Thus there exists a need for a double seam forming apparatus which overcomes the drawbacks associated with prior art systems and which is reliable and economical.
It is an object of the present invention to provide a double seam forming apparatus for applying end units to can bodies.
It is a further object of the present invention to provide a double seam forming apparatus which identifies defective can seams.
It is a further object of the present invention to provide a double seam forming apparatus that identifies particular fault conditions of a formed seam.
It is a further object of the present invention to provide a double seam forming apparatus that minimizes the risk of false fault indications.
It is a further object of the present invention to provide a double seam forming apparatus that monitors seam conditions and accounts for variations in tooling at the stations of a multi-station machine.
It is a further object of the present invention to provide a double seam forming apparatus that identifies seam imperfections even when such imperfections do not place the seam parameters outside of acceptable limits.
It is a further object of the present invention to provide a double seam forming apparatus that can be used to identify trends in seam characteristics.
It is a further object of the present invention to provide a double seam forming apparatus that can reject cans with defective seams without having to stop the operation of the apparatus.
It is a further object of the present invention to provide a double seam forming apparatus that has reduced set-up time compared to prior devices.
It is a further object of the present invention to provide a double seam forming apparatus that reduces the risk of cam failure.
It is a further object of the present invention to provide a double seam forming apparatus that is reliable and economical to operate.
Further objects of the present invention will be made apparent in the following Best Modes For Carrying Out Invention and the appended claims.
The foregoing objects are accomplished and a preferred embodiment of the invention by a double seam forming apparatus that secures and seals end units to can bodies through the formation of a double seam. These end units are generally top ends which are applied after a product has been placed in the can. Alternatively the present invention may be used in connection with the application of bottom ends which are seamed prior to placing product in the can.
The apparatus includes a cam with at least one seaming track. The seaming track includes a high dwell portion. Cam followers in operative connection with seam forming rolls and chucks engage the high dwell portion as cans undergo a final ironing turn to form the double seam.
A sensor is mounted in operative connection with the high dwell portion of the seaming track of the cam. The sensor operates to generate signals responsive to the force applied by cam followers which cause slight deformation of the cam as they move across the high dwell portion. The force applied by each cam follower on the high dwell portion is representative of the force applied by the cam forming roll and chuck to the circumferential can seam that is formed while in engaged relation therewith.
The apparatus of the preferred form of the present invention includes a cam body which is relatively rigid compared to the instrumented portion of the cam. An extending portion of the cam body engages the high dwell portion with the cam body responsive to the high dwell portion approaching its maximum permissible deflection. This might occur in a fault situation. The extending portion provides reinforcement and reduces the risk of the high dwell portion permanently deforming or fracturing.
The apparatus of the invention includes a monitoring apparatus or system. The monitoring system is in operative connection with the sensor. The monitoring system has a sampling portion that operates to sample sensor signals at a plurality of locations as the cam follower moves across the high dwell portion of the cam. This is done for the cam follower associated with each station as each can seam undergoes its final ironing turn.
The monitor system further includes a data generating portion which is operative to produce a plurality of data elements representative of a can seam profile. In a preferred form of the invention the data elements are generated by a base line reference generating portion included in the data generating portion. The base line reference generating portion subtracts from each sensed value a corresponding value in a base line profile, which base line profile is established and stored in a memory during set-up of the system. In the preferred embodiment, a can which has a seam which does not vary significantly from the base line profile produces a can seam profile that is represented by a generally straight line and which does not deviate significantly from the base line profile.
The monitoring system of the apparatus in the preferred embodiment also has an averaging portion that operates to average all the data elements that are calculated for each can seam. This average is compared to a plurality of stored threshold values. In a preferred embodiment this average is compared to threshold values stored in a limit storage portion of the monitor system, which stored values correspond to a tight fault condition, a tight warning condition, a loose fault condition and a loose warning condition. Can seam data for each can is stored in a database along with an indication of any threshold values that are crossed. Crossing threshold values for fault conditions causes a signal generating portion of the monitoring system to set a flag associated with the can identified as having a defective seam.
The monitoring system further includes a comparator portion which is operable to compare each of the data elements for the particular seam to the average of all the data elements for that seam. Variation of a particular data element above the average by more than a high set threshold amount may be indicative of high transient force associated with excess metal on a chuck, roll, or seam. Likewise, variation of a data element from the average below a set low threshold amount may be indicative of a broken seam, roll or chuck. If such a high or low variation from average is encountered a discriminating portion of the monitoring system operates to compare a number of adjacent data elements in the seam profile to verify that such condition existed for a sufficient time so as to be representative of an excess metal or broken condition rather than a transient noise signal. Upon identifying a metal or broken condition the signal generating portion the monitor system of the apparatus flags the can as having a defective condition.
The preferred embodiment of the invention further includes a feed sensor for sensing when cans are delivered to a station of the apparatus. If no can is delivered to a station a disregarding portion of the monitoring system is operative to disregard sensor readings from that station when its associated cam follower passes over the instrumented cam portion.
The preferred form of the invention also includes a reject portion which is operative to divert cans that have been flagged because they exhibit a fault condition. The reject portion is operative to divert such cans after they have passed through the machine so as to segregate defective cans from good cans without having to shut down the apparatus.